Ferritic stainless steel and steel sheet for heat pipes, and heat pipe and high-temperature exhaust heat recovery system

Abstract

Provided is a ferritic stainless steel for heat pipes of high-temperature exhaust heat recovery systems, which comprises, in terms of % by mass, from 16 to 32% of Cr, at most 0.03% of C, at most 0.03% of N, at most 3% of Si, at most 2% of Mn, at most 0.008% of S, from 0 to 0.3% of Al, and at least one of at most 0.7% of Nb, at most 0.3% of Ti, at most 0.5% of Zr and at most 1% of V, and optionally at least one of at most 3% of Mo, at most 3% of W, at most 3% of Cu, at most 0.1% of Y, at most 0.1% of REM (rare earth metal) and at most 0.01% of Ca, with a balance of Fe and inevitable impurities, and which satisfies at least the following formula (1), formula (2) and formula (5):Cr+3(Mo+Cu)≧20  (1)Cr+3(Si+Mn+Al−Ti)≧20  (2)0.037{(C+N) / (V+Ti+0.5Nb+0.5Zr)}+0.001≦0.01  (5).

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to stainless steel and steel sheets for use for heat pipes for heat exchange that harness the latent heat of evaporation of water, as well as to the heat pipe thereof and a high-temperature exhaust heat recovery system comprising it.[0003]2. Background Art[0004]Recently, a high-temperature exhaust heat recovery system is being put into practical use for the purpose of recovering the heat of engine exhaust gas to be discharged at high temperatures in vehicle driving and recycling it as an energy source for vehicles for the purpose of enhancing fuel efficiency in vehicles. In general, a heat exchanger is applied to recovery of exhaust heat, which is for heat exchange between exhaust heat and cooling water or any other heat medium; and as a method of realizing efficient heat exchange, a heat exchanger with a heat-transferring means that may be referred to as a heat pipe is being specifically n...

AI Technical Summary

Benefits of technology

[0016]An object of the present invention is to develop a ferritic stainless steel of a type of ferritic steels naturally having the above-mentioned advantages, which has the property of stably preventing the pressure increase to be caused by hydrogen generation in use thereof for vessels constituting a heat pipe, which has high-temperature oxidation resistance and high-temperature strength enough for use thereof in a temperature range of from 600 to 900° C., and which has corrosion resistance and Ni brazability suitable for heat pipes; and to provide a technique capable of constructing a heat pipe-type exhaust heat recovery system of high popularity.

[0021]According to the invention, the increase in the inner pressure of a stainless steel-made heat pipe, which is caused by hydrogen generation in the heat pipe and is problematic therein, can be significantly relieved. Using the heat pipe can realize a high-temperature exhaust heat recovery system of high popularity at a low cost, therefore contributing toward further popularization of exhaust heat recovery systems in vehicles, etc.

Problems solved by technology

However, a heat pipe formed of stainless steel may have a large quantity of hydrogen generated inside it in the early stage of driving.

In addition, the hydrogen generation inside the heat pipe is a risk factor of lowering the heat transfer efficiency to cooling water and is additionally a risk factor of imparting excessive stress to the system; and therefore this may be a remote cause of system damage and heavy disasters.

On the negative side, a ferritic stainless steel is generally inferior to austenitic steels in point of high-temperature oxidation resistance, high-temperature strength, corrosion resistance, etc.

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