Blockchain technology for Industry 4.0 applications research investigates how decentralized ledger systems can enhance automation, security, and transparency in smart manufacturing and cyber-physical industrial ecosystems. Research papers in this domain explore applications such as secure machine-to-machine communication, supply chain traceability, decentralized production management, predictive maintenance, and autonomous quality control. Studies highlight the use of smart contracts to automate industrial workflows, enforce operational rules, and manage transactions without intermediaries, while cryptographic techniques ensure data integrity, confidentiality, and provenance. Challenges addressed include scalability to handle high-frequency industrial data, interoperability with legacy systems, latency constraints for real-time operations, and resource limitations of edge devices in Industry 4.0 setups. Proposed solutions often combine lightweight consensus protocols, hybrid blockchain architectures, and integration with IoT, edge, and cloud computing frameworks to optimize performance and security. Overall, this research demonstrates how blockchain provides a resilient, transparent, and secure framework for Industry 4.0, enabling efficient, trustworthy, and intelligent industrial processes.