JPS60215745A - Material for prehardened mold for casting metal having high melting point - Google Patents

Abstract

PURPOSE:To obtain the titled material having superior weldability and not causing heat cracking, melt fracture and warping by adding a small amount of B to low or medium C - low Si-Mn-Cr-Mo(W)-V(Nb)-(Ni) steel. CONSTITUTION:The titled material adjusted to HB 170-331 by refining consists of 0.16-0.28% C, <=0.60% Si, 0.10-0.90% Mn, 0.50-1.50% Cr, W and/or Mo satisfying 1/2W+Mo=0.10-0.70%, 0.03-0.30% Nb and/or V, 0.001-0.010% B and the balance Fe. The material may further contain 0.10-0.90% Ni. The material is provided with strength by which it withstands thermal stress as well as especially high heat conductivity by effectively utilizing a hardenability improving effect produced by said small amount of B, but excess hardness is not given by hardening. The material has especially superior bainite hardenability and high weldability and does not cause seizing, melt fracture and cracking even during heating. It is suitable for a large-sized mold.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pre-hardened material that is used for casting high-melting point metals such as iron-based alloys that are subject to severe thermal shock and erosion, and provides a long service life. It is characterized by being suitable for uses that require high performance.

In high-temperature iron-based alloy mold casting, heat cracks mainly occur in thin-walled areas due to large thermal shocks.

Erosion of protrusions, warping of molds related to the balance between thermal stress and strength due to temperature gradients, and elution of runners.

Settling is a major problem, and even when using general hot tool materials, the thermal conductivity is insufficient. 1. Due to cracking due to excessive increase in hardness when subjected to local area hardening effect, It may be difficult to meet the required usage performance.

On the other hand, we use mild cast steel, forged materials, and cast iron, which have relatively high thermal conductivity, to quickly diffuse the heat received from the molten metal into the mold, suppressing excessive local temperature rise, and reducing thermal stress. Although there are attempts to prevent warping, the strength is low (and it is often difficult to prevent heat cracks and warping.

The present invention has low medium C and low 8i -Mn -Cr -Mo
(W) -v(Nb) Aluminum has low Si -Mn -N
i-Cr-Mo(W)-V(Nb'.

It has a B-added composition, effectively utilizes the hardenability improvement effect of a small amount of B added, and has particularly high thermal conductivity as well as strength that can withstand thermal stress, resulting in excessive hardening hardness. and has particularly excellent bainitic hardenability.
It has good weldability, has a small tendency to locally raise the temperature to high temperatures, and even when the temperature rises, it does not cause seizure or melting damage.

It provides a pre-hardened mold material suitable for large molds. □ Table 1 shows examples of the composition of the steel of the present invention and its hardness when quenched at 2.5 m semi-cooled from a quenching temperature of 940°C. .

The steel of the present invention is difficult to martensitic, has a strong tendency to bainitic quench hardening, does not exhibit excessive quench hardness values, and has semi-cooled 2,
At 5-, no excessive decrease in quenching hardness occurs.

Table 1: In other words, bainite hardenability is high. This has extremely important meanings, such as uniform hardening inside and outside the mold, reduced susceptibility to cracking when subjected to the re-hardening effect due to temperature rise during use, and improved weldability.

Table 2 shows the thermal conductivity of the steel of the present invention. The steel of the present invention has a higher thermal conductivity than Comparative 1111 (SKD61), and has a thermal conductivity comparable to Comparative Steel (2) (low carbon steel). In general, it is difficult to simultaneously improve hardenability and maintain thermal conductivity at a high level, but by adding a small amount of B, the level of addition of elements such as Ni, Mn, and Cr can be kept low. Its major feature is that it provides sufficient hardenability in the state of heat and has excellent thermal conductivity.

Table 3 It can be seen that the present invention S maintains a strength similar to that of the comparative sr (8KD61), and has a much higher room temperature to high temperature tensile strength than the comparative steel TI (low carbon steel). C' is shown for reference when a steel with the same composition as the invention steel C is heat treated to a low heat treatment hardness of HBO2,O, and when the heat treatment hardness is low, compared to low carbon steel A sufficient improvement in high temperature strength cannot be obtained.

Table 4 shows the 1550"C molten metal dripping test of 1scr #1 using a flat test piece, tilted at 30 degrees with respect to the horizontal surface, and the time until the onset of seizure when 5g of molten metal was repeatedly dropped from a height of ioam onto this surface. The number of repetitions of Comparative Steel I is set as 100 and is expressed as an index.

The steel of the present invention is comparative steel 1. It can be seen that the molten metal seizure resistance is superior to that of I[. This is due to the fact that it has particularly excellent thermal conductivity while maintaining high-temperature strength similar to Comparative #fI, which is a major feature of the great invention steel. On the other hand, Comparative Steel I Although the thermal conductivity itself is high, the seizure resistance is slightly lower than that of Comparative Steel I.This has high thermal conductivity, but on the contrary, high-temperature strength is low, and corrosion due to thermal stress due to dripping of molten metal, This is because it could not withstand the seizure effect.

Table 5 shows that a mold release agent was applied to a heat crack test piece (length: 70 mm) with a tip angle of 40° (rust shape), and an i
The average number, average depth, and maximum depth of cracks that occurred in the direction perpendicular to the length of the tip when the operation of immersing the tip in molten sCr stainless steel for 3 seconds and then cooling it in air was repeated 200 times. ◎Table 5 It can be seen that the steel of the present invention clearly has better heat check resistance than comparative steels I and n. This is because the addition of a small amount of B increases hardenability without reducing thermal conductivity, resulting in excellent strength at room temperature to high temperature.・C
' shows the behavior when a material having the same composition as Oka C of the present invention is heat treated to a low hardness. It can be seen that if the heat treatment hardness is excessively low, it is difficult to exhibit the original heat crack resistance properties. Considering usability such as heat crack resistance, resistance to mold warping, and machinability, the appropriate hardness range is HB170 to HB351.

Next, the reason for limiting the composition of the steel of the present invention will be described.

C is quench hardened to the steel of the present invention, and during tempering, Cr, M
A special carbide is formed and precipitated between O, W, V, etc., and has the continued softening resistance necessary for the mold for this purpose.

Setting the amount of C is extremely important in order to maintain the characteristics of the steel of the present invention, which is necessary to obtain strength at room temperature and high temperature, and is sufficiently hardened even when the mold size is large. If it is too low, the above effects cannot be obtained, so it should be set at 0.16% or more, and if it is too high, it will reduce weldability, as well as thermal conductivity and thermal shock resistance, so it should be set at 0.28% or less. A more desirable range of C is 0.18-026%.

The content of Si is desirably lower in terms of increasing thermal conductivity.

In addition, it is necessary to limit the temperature to a low level in order to effectively form an oxide film on the mold surface due to temperature rise during use and prevent seizure of the molten metal. Low Si is one of the important features of the steel of the present invention. In 8i, it is necessary to contain a certain amount of maracin for steelmaking work, and from the viewpoint of the above effects, the permissible limit is 0.60%.
The following shall apply. The desirable range of Si is 0.035% or less.

Mn forms a solid solution in the matrix and is added to provide the excellent hardenability that is a feature of the steel of the present invention. If it is too low, the effect of addition cannot be obtained, so it should be 0.10% or more, and if it is too high, A,
It lowers the transformation point, resulting in a decrease in weldability and thermal conductivity, so it is set to 090% or less.

Generally, Mn is desirably 0.70% or less.

Like Mn, Ni forms a solid solution in the matrix and is added to provide the excellent hardenability characteristic of the steel of the present invention.

If it is too low, the effect of addition cannot be obtained, so it should be 0.10% or more, and if it is too high, it will lower the transformation point, resulting in a decrease in weldability and thermal conductivity, so it should be 0.90% or less.〇Generally N
It is desirable that i be 0.70% or less.

Cr improves hardenability and forms special carbide with C.
Necessary to increase softening resistance and provide high temperature strength. Similar to Mn, Ni, and Mo, setting the content is extremely important in order to provide the steel of the present invention with excellent hardenability. If it is too low, the effect of the above addition cannot be obtained, so the setting value is 0.
It should be 50% or more, and if it is too high, weldability will be excessively reduced.
It also causes a decrease in thermal conductivity, making it difficult to maintain the characteristic of the steel of the present invention, which is particularly good thermal conductivity, so it is set at 1.50% or less. Cr is generally desirably 1.30% or less).

MO is one of the most important elements for improving hardenability, forming a special carbide with C, increasing softening resistance, and imparting high-temperature strength.

W has the same effect as MO, but MO is advantageous in terms of improving hardenability and toughness, and W is advantageous in terms of high-temperature strength.
o and W are used together. If it is too low, the effect of the above addition cannot be obtained, so 1/2 WX Mo should be set at 0.10% or more, and if it is too high, the thermal conductivity and toughness will decrease.

0.70 for 1/2W+Mo, as this will lead to a decrease in weldability.
% or less. Generally, the desirable range is 1/2W-1
-M.

O V, Nb, which is 0.20-060%, leads to refinement of crystal grains and improves impact resistance, and also forms and precipitates special carbides between carbon and softening resistance during tempering. Added to increase high temperature strength. Nb is more advantageous in terms of the effect of improving high-temperature strength properties, while V is more advantageous in terms of toughness, and they are used depending on the purpose and application. If it is too low, the effect of the above addition cannot be obtained, so one or two of V or Nb is added to 0.
．． If it is too high, coarse carbides will be formed,
Similarly, one or two of V or Nb may cause a decrease in toughness, hardenability, and thermal conductivity.
The amount shall be ¥0.30% or less. In general, the desirable range of V-)-Nb is 0.005% to 0.20%. , provides excellent room temperature and high temperature strength,
The most important elements for forming wood-like characteristics
It is.

If it is too low, the hardenability improvement effect cannot be obtained, so 0.001
% or more, and if it is too high, hot workability will be reduced, so 0
．． 0.010%@-Generally, the desirable range of B is 0.010%.
002% to 0.007%.

As described above, the steel of the present invention has a low to medium C and a low to 8i
-Mn -Cr -Mo (W) -V (Nb) or -low8i -Mn -Ni -Cr -Mo (9
V) -'V(Nb) has a composition with the addition of B, and has an extremely high bainite hardenability (in particular, it hardens both internally and externally even in large molds, and causes excessive quench hardening. Despite its high hardenability, it has excellent weldability.
Even when subjected to the quenching effect due to local excessive temperature rise during use, it does not cause cracking, and its high thermal conductivity, high-temperature strength, excellent oxide film properties, and toughness prevent melting and seizure. , heat crack.

The present invention provides a new pre-hardened mold material for high melting point metal casting that does not cause warping and has a long life.

Claims (1)

[Claims] 1. CO, 16-0.28%, 8i 0.60% or less, 9Mn 0.10-0.90%, Cr 0.50-0.
010 W, containing Mo alone or in combination, 1/2
W+Mo is 0.10~0.70%, Nb or V inside 1 Seed Mat, :-ha2 Seed 005~0.010, B
A pre-hardened type material for casting high melting point metals, consisting of O,001~'0.010% balance Fe and normal impurities, tempered to HB170~331. 2, CO, 16-0.28%, Si 060% or less,
Mno, 1o~0.90%, NiO, 10~
0.010 CrO, 50-1.50%, W. Contains MO alone or in combination and 1/2W+Mo is 0.1
0 to α70%, 0 to 1 or 2 of Nb or ■
．． 05~0.30%, BO,001~0.010
% balance consists of Fe and normal impurities, HB170 ~
Pre-hardened material for casting high melting point metals tempered to 331.