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The susceptibility of Advanced High Strength Steels (AHSS) to hydrogen embrittlement (HE) was evaluated on selected high strength sheet steels (DP 600, TRIP 780, TRIP 980, TWIP-Al, TWIP, and Martensitic M220) and the results were compared to data on a lower strength (300 MPa tensile strength) low carbon steel. Tensile samples were cathodically charged and then immediately tensile tested to failure to analyze the mechanical properties of the as-charged steel. The effects of hydrogen on deformation and fracture behavior were evaluated through analysis of tensile properties, necking geometry, and SEM images of fracture surfaces and metallographic samples of deformed tensile specimens. The two fully austenitic TWIP steels were resistant to hydrogen effects in the laboratory charged tensile samples.

Fracture split forged steel connecting rods are utilized in many new high performance automotive engines to increase durability. Higher strength levels are needed as the power density increases. Fracture splitting without plastic deformation is necessary for manufacturability. Metallurgical design is a key for achieving the required performance levels. Several medium carbon steels containing 0.07 wt pct P, 0.06 wt pct S and various amounts of Mn, Si, V, and N were produced by vacuum induction melting laboratory heats and hot working the cast ingots into plates. The plates were cooled at varying rates to simulate typical cooling methods after forging. Microstructures were generally ferrite and pearlite as evaluated by light optical and scanning electron microscopy. Mechanical properties were determined by standard tensile tests, high strain rate notched tensile tests, and Charpy V-notch impact tests to assess “splittability”.

Quenching and partitioning (Q&P) is a novel heat treatment to produce third generation advanced high-strength steels (AHSS). The influence of carbon on mechanical properties of Q&P treated CMnSi-steels was studied using 0.3C-1.5Mn-1.5Si and 0.4C-1.5Mn-1.5Si alloys. Full austenitization followed by two-step Q&P treatments were conducted using varying partitioning times and a fixed partitioning temperature of 400 °C. The results were compared to literature data for 0.2C-1.6Mn-1.6Si, 0.2-3Mn-1.6Si and 0.3-3Mn-1.6Si Q&P treated steels. The comparison showed that increasing the carbon content from 0.2 to 0.4 wt pct increased the ultimate tensile strength by 140 MPa per 0.1 wt pct C up to 1611 MPa without significantly decreasing ductility for the partitioning conditions used. Increased alloy carbon content did not substantially increase the retained austenite fractions. The best combinations of ultimate tensile strength and total elongation were obtained using short partitioning times.

An iterative learning control (ILC) algorithm has been developed for a test cell electro-hydraulic, fully flexible valve actuation system to track valve lift profile under steady-state and transient operation. A dynamic model of the plant was obtained from experimental data to design and verify the ILC algorithm. The ILC is implemented in a prototype controller. The learned control input for two different lift profiles can be used for engine transient tests. Simulation and bench test are conducted to verify the effectiveness and robustness of this approach. The simple structure of the ILC in implementation and low cost in computation are other crucial factors to recommend the ILC. It does not totally depend on the system model during the design procedure. Therefore, it has relatively higher robustness to perturbation and modeling errors than other control methods for repetitive tasks.

The influence of coatings on fatigue behavior has been examined for the following commercially produced sheet steels: uncoated titanium stabilized interstitial-free (IF); electrogalvanized titanium stabilized IF; hot-dip galvanized aluminum killed, drawing quality (AKDQ); and galvannealed AKDQ. Fully reversed bending fatigue tests were conducted at ambient temperature on Krouse-type flexural fatigue machines. A dependence of crack development was observed and correlated to the microstructure and properties of the different coatings. Furthermore, a functional design relationship for each material was determined through stress-life analysis. The experimentally determined fatigue properties were compared to conventional estimates based on tensile properties which ignore coating effects. The results of this work suggest that ductile coatings may enhance fatigue resistance, while brittle coatings may reduce fatigue life.

Fine water mist has become a commercial technology for fire suppression in multiple applications. With funding from NASA, ADA Technologies, Inc. (ADA) is developing a handheld fine water mist fire extinguisher for use on manned spacecraft and in future planetary habitats. This design employs only water and nitrogen as suppression agents to allow local refill and reuse. The prototype design incorporates features to generate a uniform fine water mist regardless of the direction of the gravitational vector or lack of gravity altogether. The system has been proven to extinguish open fires and hidden fire scenarios in tests conducted at the Colorado School of Mines (CSM). This design can be deployed as a portable extinguisher or as an automated system for local fire protection in instrument racks or storage spaces. Continued development will result in prototype hardware suitable for use on future manned spacecraft.

Direct osmotic concentration (DOC) is an integrated membrane treatment process designed for the reclamation of spacecraft wastewater. The system includes forward osmosis (FO), membrane evaporation, reverse osmosis (RO) and an aqueous phase catalytic oxidation (APCO) post-treatment unit. This document describes progress in the third year of a four year project to advance hardware maturity of this technology to a level appropriate for human rated testing. The current status of construction and testing of the final deliverable is covered and preliminary calculations of equivalent system mass are funished.

ADA Technologies, Inc. has designed and built a microgravity-tolerant portable fire extinguisher prototype for use in manned spacecraft and planetary habitats. This device employs Fine Water Mist (FWM) as the fire extinguishing agent, and is refillable from standard stores on long-duration missions. The design uses a single storage tank for minimal mass and volume. The prototype employs a dual-fluid atomizer concept where the pressurant gas (nitrogen) also enhances the water atomization process to generate a droplet size distribution in the optimum diameter range of 10 to 50 micrometers. The expanding discharge gas plume carries the mist to the immediate vicinity of the fire where its extensive surface area promotes high heat transfer rates. A series of 80 fire suppression tests was recently completed to evaluate design options for the hardware and validate performance on three representative fire scenarios.

With the increased use of tubular steel products, especially for automotive hydroforming applications, there is increased interest in understanding the mechanical properties measured by tensile tests from specimens of different orientations in the tube. In this study, two orientations of tensile specimens were evaluated -- axial specimens with and without flattening and flattened circumferential specimens. Three steels were evaluated -- two thicknesses of aluminum killed drawing quality (AKDQ) steel and one thickness of high strength low alloy (HSLA) steel. Mechanical property data were obtained from the flat stock, conventional production tubes and quasi tubes. Quasi tubes were produced from the flat stock on a 3-roll bender, but the quasi tube was not welded or sized.

The response of HSLA steel, 590R, and dual-phase steel, DP-600, to non-uniform deformation imposed in a laboratory Bending-Under-Tension (BUT) test apparatus was evaluated. Samples were deformed with both low and high back tension forces at bend angles of 45 and 90 degrees, and evaluated to determine the “side-wall curl”, i.e. the curvature in the sheet section in contact with the die. The results indicate that there are no consistent differences between the two steels, 590R and DP-600. It was found that back tension, tensile strength and sheet thickness were the primary factors affecting curl. The bend angle has an influence on curl, with the curl radius at a 90° bend angle being greater than the curl radius at a 45° bend angle.

The effectiveness of three different techniques, designed to improve the bending fatigue life in comparison to conventionally processed gas-carburized 8620 steel, were evaluated with modified Brugger bending fatigue specimens and actual ring and pinion gears. The bending fatigue samples were machined from forged gear blanks from the same lot of material used for the pinion gear tests, and all processing of laboratory samples and gears was done together. Fatigue data were obtained on standard as-carburized parts and after three special processing histories: shot-peening to increase surface residual stresses; double heat treating to refined austenite grain size; and vacuum carburizing to minimize intergranular oxidation. Standard room-temperature S-N curves and endurance limits were obtained with the laboratory samples. The pinions were run as part of a complete gear set on a laboratory dynamometer and data were obtained at two imposed torque levels.

Quenching & Partitioning (Q&P) is receiving increased attention as a novel Advanced High Strength Steel (AHSS) processing route as promising tensile properties of the “third generation” have been reported. The current contribution reports hole expansion ratios (HER) of Q&P steels and compares the values with HERs obtained for “conventional” AHSS processing routes such as austempering and Quench & Tempering (Q&T). Intercritically annealed C-Mn-Al-Si-P and fully austenitized C-Mn-Si microstructures were studied. Optimum combinations of tensile strength and HER were obtained for fully austenitized C-Mn-Si Q&P samples. Higher HER values were obtained for Q&P than for Q&T steels for similar tempering/partitioning temperatures. Austempering following intercritical annealing results in higher HER than Q&P at similar tensile strength levels. In contrast, Q&P following full austenitization results in higher hole expansion than austempering even at higher strength levels.

Punch-stretch tests to determine formability of type 304 stainless steel sheet were conducted using a hemispherical dome test. Sheets of 19.1 mm width and 177.8 mm width were stretched on a 101.6 mm diameter punch at punch rates between 0.042 to 2.12 mm/sec with three lubricant systems: a mineral seal oil, thin polytetrafluoroethelyne sheet with mineral seal oil, and silicone rubber with mineral seal oil. The resulting strain distributions were measured and the amount of martensite was determined by magnetic means. Increasing lubricity resulted in more uniform strain distributions while increased punch rates tended to decrease both strain and transformation distributions. High forming limit values were related to the formation of high and uniformly distributed martensite volume fractions during deformation. The results of this study are interpreted with an analysis of the effects of strain and temperature on strain induced martensite formation in metastable austenitic stainless steels.

Five heats of vanadium-microalloyed steel with carbon contents from 0.29% to 0.40% and sulfur contents from 0.031% to 0.110% were forged into automotive spindles and air cooled. Three of the steels were continuously cast whereas the other two were ingot cast. The forged spindles were subjected to microstructural analysis, mechanical property testing, full component testing and machinability testing. The microstructures of the five steels consisted of pearlite and ferrite which nucleated on prior austenite grain boundaries and predominantly on intragranularly dispersed sulfide inclusions of the resulfurized grades. Ultimate tensile strengths and room temperature Charpy V-notch impact toughness values were relatively insensitive to processing and compositional variations. The room temperature tensile and room-temperature impact properties ranged from 820 MPa to 1000 MPa (120 to 145 ksi) and from 13 Joules to 19 Joules (10 to 14 ft-lbs), respectively, for the various steels.

The influences of laboratory-induced hydrogen on the tensile deformation and fracture behavior of selected sheet steels including conventional DQSK and HSLA steels as well as newer DP and TRIP grades were evaluated. The effects of cold work, simulated paint baking, and natural aging were considered. Hydrogen effects were observable by increased flow stress, decreased ductility, altered neck geometry, and altered fracture mechanisms. Differences among the steels and conditions were observed and interpreted on the basis of microstructure, fracture behavior, and theories of hydrogen embrittlement.

High strain rate sheet tensile tests (up to 300s-1) and Ohio State University (OSU) formability tests (up to an estimated strain rate of 10s-1) were performed to examine the effect of strain rate on the mechanical properties and formability of five ferritic stainless steels: HIGH PERFORMANCE-10™ 409 (HP-10 409), ULTRA FORM® 409 (UF 409), HIGH PERFORMANCE-10™ 439 (HP-10 439), two thicknesses of 18 Cr-Cb™ stainless steel, all supplied by AK Steel, and Duracorr®, a ferrite-tempered martensite dual-phase stainless steel supplied by Bethlehem Steel Corporation. Tensile results show that increasing strain rate resulted in increases in yield stress, flow stress, and stress at instability for all alloys tested. In addition, increases in uniform and total elongation were also found for each of the five alloys.

The bending fatigue performance of gears, cantilever beam specimens, and notched-axial specimens were evaluated and compared. Specimens were machined from a modified SAE-4118 steel, gas-carburized, direct-quenched and tempered. Bending fatigue specimens were characterized by light metallography to determine microstructure and prior austenite grain size, x-ray analysis for residual stress and retained austenite measurements, and scanning electron microscopy to evaluate fatigue crack initiation, propagation and overload. The case and core microstructures, prior austenite grain sizes and case hardness profiles from the various types of specimens were similar. Endurance limits were determined to be about 950 MPa for both the cantilever beam and notched-axial fatigue specimens, and 1310 MPa for the single gear tooth specimens.

The effects of subzero treatments on the bending fatigue performance of carburized gear steels were investigated by cantilever bending fatigue testing. Specimens were machined from SAE-4320 and SAE-9310 bar stock steel, gas-carburized, quenched, tempered at 175°C, subzero cooled to -73°C and -196°C, and tempered at 175°C. Bending fatigue specimens were characterized by light metallography to determine microstructure and prior austenite grain size, x-ray diffraction for residual stress and retained austenite contents, microhardness testing, and scanning electron microscopy to evaluate fatigue crack initiation, propagation and overload. Refrigeration treatments caused additional transformation of retained austenite and increased surface hardness and compressive residual stresses. Bending fatigue endurance limits for the SAE-4320 specimens were determined to be 1310 MPa for the as-carburized condition, 1170 MPa for the -73°C condition, and 1280 MPa for the -196°C condition.

This project investigated the effect of carburizing carbon-potential and thermal history on the bending fatigue performance of carburized SAE 4320 gear steel. Modified-Brugger cantilever bending fatigue specimens were carburized at carbon potentials of 0.60, 0.85, 1.05, and 1.25 wt. pct. carbon, and were either quenched and tempered or quenched, tempered, reheated, quenched, and tempered. The reheat treatment was designed to lower the solute carbon content in the case through the formation of transition carbides and refine the prior austenite grain size. Specimens were fatigue tested in a tension/tension cycle with a minimum to maximum stress ratio of 0.1. The bending fatigue results were correlated with case and core microstructures, hardness profiles, residual stress profiles, retained austenite profiles, and component distortion.

This study evaluated the bending fatigue performance of a modified SAE 4320 steel as a function of carburizing technique. S-N curves and endurance limits were established by fatigue testing modified Brugger-type specimens that are designed to simulate a single gear tooth. Fractured specimens were examined by light and electron microscopy to determine crack initiation sites, establish the extent of stable crack propagation, and analyze surface oxide types and distributions. Test results show that plasma-carburizing boosted the endurance limit of an oxidation-susceptible gear steel from 1100 MPa to 1375 MPa. Fatigue endurance limits in excess of 1400 MPa had previously been achieved in gas-carburized SAE 4320 steels by reheat treatments and reductions in high-oxidation potential elements. The level of improvement observed in this study suggests that any of these advanced processing techniques can allow significant size reductions and weight savings in automotive transmission gears.