Experimental Studies of Thermophysical Properties and Microstructure of X37CrMoV5-1 Hot-Work Tool Steel and Maraging 350 Steel

Abstract

Measurements of thermal diffusivity, heat capacity and thermal expansion of X37CrMoV5-1 (1.2343) hot-work tool steel and Maraging 350 (1.6355) steel in the temperature range from −50 °C to 1000 °C were carried out in this paper. Both X37CrMoV5-1 and Maraging 350 are tested for military use as barrel steels. Thermophysical properties were tested using specialised test stands from NETZSCH. Thermal diffusivity was studied using both the LFA 427 laser flash apparatus in the temperature range of RT–1000 °C and the LFA 467 laser flash apparatus in the temperature range of −50 °C–500 °C. Specific heat capacity was investigated using a DSC 404 F1 Pegasus differential scanning calorimeter in the range RT–1000 °C, and thermal expansion was investigated using both a DIL 402 Expedis pushrod dilatometer in the range −50 °C–500 °C and a DIL 402 C in the range RT–1000 °C. Inconel 600 was selected as the reference material during the thermal diffusivity test using LFA467. Tests under the light microscope (LM), scanning electron microscopy (SEM) and Vickers microhardness measurements were carried out to detect changes in the microstructure before and after thermophysical measurements. This paper briefly characterises the research procedures used. In conclusion, the results of testing the thermophysical properties of X37CrMoV5-1 hot-work tool steel and Maraging 350 steel are compared with our results on 38HMJ (1.8509), 30HN2MFA and Duplex (1.4462) barrel steels. The thermophysical properties of X37CrMoV5-1 (1.2343) hot-work tool steel and Maraging 350 (1.6355) steel are incomplete in the literature. The paper presents the thermophysical properties of these steels over a wide range of temperatures so that they can be used as input data for numerical simulations of heat transfer in cannon barrels.

Some problems related to thermophysical properties of selected barrel steels

“…The apparent specific heat as a function of temperature for these steels shows small peak values: for DUPLEX steel, at a temperature of approximately 530.1℃, chromiumrich ferrite, i.e. the ' phase, dissolves and a peak appears, for MARAGING 350 steel, at least four appear peaks: 470.4℃, 547.5℃, 697.6℃, 734.9℃, the nature of which is explained in [5,6]. A separate problem is the method of calculating the thermophysical properties of barrel steels in order to obtain input data for the simulations of heat transfer in the barrel wall [8].…”

“…The proposed approximation of the specific heat capacity formula for the X37CrMoV5-1 hot-work tool steel has the following form [5,8]:…”

“…The subject of analysis were 5 types of barrel steels: 38HMJ with a density of 7.65 g/cm 3 at RT, 30HN2MFA with a density of 7.75 g/cm 3 at RT, X37CrMoV5-1 hot-work tool steel with a density of 7.75 g/cm 3 at RT, DUPLEX 2205 with a density of 7.72 g/cm 3 at RT and Maraging 350 with a density of 8.05 g/cm 3 at RT. The chemical composition of these steels is given in table 1 [4][5][6]. 38HMJ steel is an alloy steel that, thanks to the nitriding process, obtains increased surface hardness and corrosion resistance without the need for additional heat or electrochemical treatment.…”

“…It is now used as steel for hunting gun barrels [6]. X37CrMoV5-1 hot-work tool steel is highly alloyed steel, designed to work at elevated temperatures [5]. MARAGING 350 is a low-carbon iron-nickel martensitic steel hardened by precipitations of intermetallic phases [5].…”

“…a, k, cp and ρ of selected barrel steels, i.e. 38HMJ (1.8509), 30HN2MFA, X37CrMoV5-1 hot-work tool steel (1.2343), DUPLEX (1.4462) and MARAGING 350 (1.6355) in the temperature range from room temperature (RT) to 1000℃, which were measured by the authors [1,[4][5][6]. Another problem raised in the paper concerns the apparent specific heat that we get from the DSC measurement and the dependence of the specific heat on temperature in the form that we use for the numerical simulations of heat transfer in cannon barrels.…”