Concerning tensile strength, strain rate sensitivity is quite similar for each steel grade with a ratio between dynamic ( ε& = 1100s-1) and quasi-static tensile strength comprised between 1.10 and 1.24 (Figure 3). The strain rate dependency of the uniform elongation shown in Figure 4 underlines the high ductility of the austenitic stainless steel 301LN compared to the other steel grades. Even at ε& = 1100s-1 the uniform elongation of 301LN is close to 50% and the tensile curve still presents a pronounced strain hardening. 300 400 500 600 700 800 900 1000 1100 0.001 0.01 0.1 1 10 100 1000 10000 strain rate ε° (s-1) Tensile Strength (MPa) -40°C Room Temp. +80°C 301LN DP500G ZStE420 IFHSS260 Figure 3: Influence of strain rate and temperature on the tensile strength of investigated steel grades Influence of strain rate and temperature The influence of strain rate and temperature in the range -40°C to +80°C defines stress domains in function of strain rate with an upper limit for -40°C describing a combined effect of strain rate and low temperature and a lower limit expressing the strain rate effect balanced by the higher temperature. Over the investigated range of strain rates the ferritic steels and DP500G are characterised by a maximum decrease of 50MPa for the lower yield strength or tensile strength at +80°C compared to room temperature. The increase of the lower yield strength noted at -40°C shows higher strain rate sensitivity due to a combined effect of temperature and strain rate (Figures 3, 4). The strain rate dependency of the uniform elongation, shown on Figure 4, is quite similar for ZStE420 and IFHSS260 with a higher reduction at -40°C compared to room temperature and a nearly constant value at 80°C. It must be noted that the dual phase steel DP500G did not show any increase or reduction in uniform elongation within the investigated temperature range, at least up to ε& = 10s-1. So, only the results at room temperature are presented in Figure 4. 0 10 20 30 40 50 60 0.001 0.01 0.1 1 10 100 1000 10000 strain rate ε° (s-1) Uniform Elongation (%) -40°C Room Temp. +80°C 301LN IFHSS260 ZstE420 DP500G Figure 4: Influence of strain rate and temperature on the uniform elongation of investigated steel grades The influence of strain rate and temperature on 301LN stainless steel is quite different due to the strain induced austenite to martensite (γ→α’) transformation. The austenitic steel is very sensitive to temperature
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